Field of the Invention
The present invention relates to a lighting control technology designed for a vehicle headlamp.
Description of the Background Art
Conventional examples of a vehicle headlamp include a headlamp that generates white light by causing light emitted from a laser diode to enter a fluorescent substance while scanning the light using a micro electro mechanical systems (MEMS) mirror or the like, and uses the light to illuminate an area in front of the vehicle. (For example, refer to Japanese Translation of PCT International Application Publication No. JP-T-2013-526759.) Further, a vehicle headlamp having a configuration in which a laser beam emitted from a semiconductor laser is made to directly enter a fluorescent substance without being scanned, causing the luminous body to emit light, is also known. (For example, refer to Japanese Unexamined Patent Application Publication No. 2014-022069.)
However, because the light of the laser diode used in the vehicle headlamp having such a configuration as described above has a relatively high output, a countermeasure is required to ensure that the light of the laser diode does not leak externally when the vehicle headlamp is damaged due to a vehicle collision or the like or when the fluorescent substance is otherwise damaged, detached, or the like. In this regard, it is also conceivable to continually detect an output state of the laser diode by a photodiode, and suspend operation of the laser diode if an abnormality occurs, for example.
However, because of problems in an operating speed of an electronic circuit, a relatively long time is required from abnormality detection by the photodiode to suspension of laser diode operation. Although dependent on the characteristics of the electronic circuit used and the like, the time required from abnormality detection to suspension of laser diode operation is in the order of several microseconds while the permissible exposure time of the laser diode is in the order of from several tens to several hundreds of nanoseconds, resulting in the possibility that the output light from the laser diode will leak externally as a result of damage to a housing of the vehicle headlamp.
Thus, technology that turns off the laser diode more quickly when an abnormality occurs is desired. Further, such a need is not limited to use of a laser diode as the light source, and can also similarly arise with use of a light source having relatively high light output intensity as well.
It is therefore one object of specific aspects according to the present invention to provide lighting control technology that, when an abnormality occurs in a vehicle headlamp that uses a light source having high output intensity, is capable of quickly turning off the light source.